1. G. T. Hahn, R. C. Hoagland, and A. R. Rosenfield: AF 33615-70-C-1630, Bat-telle Memorial Institute, Columbus, Ohio, August, 1971.
2. J. M. Barsom, E. J. Imhof, and S. T. Rolfe: ARL-B-23103, U. S. Steel Corp., Monroeville, Pennsylvania, 1968.
3. J. F. Throop and G. A. Miller:Amer. Soc. Test. Mater., Spec. Tech. Publ. 467, p. 154, American Society for Testing and Materials, 1969.
4. R. C. Bates and W. G. Clark: 68-1D7-RPAFC-P1, Westinghouse Research Lab-oratories, Pittsburgh, Pennsylvania, 1968.
5. G. A. Miller:Trans. ASM, 1969, vol. 62, p. 651.